The thermal properties of polymer materials have always been an important parameter of material properties, determining the use of materials, and can also be used for industrial quality control and product development. In general, the glass transition temperature is the upper temperature limit for the use of thermoplastics and is the lower limit temperature for the use of rubber or elastomer.
1. The difference between crystalline polymer and amorphous polymer
An amorphous polymer, also known as an amorphous polymer, has a molecular shape and a polymer in which the molecules are arranged in a disordered state. For an amorphous or amorphous polymer, the amorphous is too equivalent to an amorphous state.
The regularly arranged region of the crystalline polymer is called a crystal region, and the disordered region is called an amorphous region. The percentage of the crystal region is called crystallinity. Generally, a polymer having a crystallinity of 80% or more is called crystalline polymerization. Things.
Most of the polymers have a crystalline portion and an amorphous portion, and the ratio of the crystalline portion to the amorphous portion is called crystallinity.
2, high polymer glass state, high elastic state, viscous flow state and Tg
The relationship between the deformation state of the product and the temperature change of the polymer under a constant pressure. In the low temperature range, the polymer is rigid and has a small deformation with external force. The state is similar to glass, which is called glass state. When the temperature rises to a specific interval, the deformation is obvious under the action of external force and the temperature change is relatively stable with a certain temperature range. It is called high elastic state; when the temperature rises to the high polymer to form a viscous fluid, the deformation cannot be recovered, which is called a viscous flow state.
3. The main factors affecting the glass transition temperature (Tg)
(1) Molecular chain flexibility: The greater the flexibility of the molecular chain, the lower the glass transition temperature (Tg); the greater the molecular weight rigidity, the higher the glass transition temperature (Tg).
(2) cross-linking: cross-linking of polymer molecules, reducing free volume, hindered movement of molecular chains, reduced flexibility, and increased glass transition temperature (Tg);
(3) Molecular weight: The molecular weight is small, and the influencing factor is obvious. When the molecular weight exceeds a certain level, the glass transition temperature (Tg) is not significantly changed with the molecular weight.
(4) Plasticizer: The plasticizer has a significant influence on the glass transition temperature. The glass transition temperature is higher, and the glass transition temperature (Tg) is significantly lowered after the addition of the plasticizer.
(5) Ionic bond: Introduced into the polymer chain, the glass transition temperature (Tg) can be significantly increased.
4, glass transition temperature product application
Taking the glass transition temperature (Tg) of acrylic resin as an example, according to the comprehensive requirements of coating type, performance and special performance, the specific conditions are as follows:
The higher the Tg, the harder the smear and the stronger the scratch resistance, but the application is not brittle; at the same time, after the lacquering, the better the surface of the coating is, the faster the solvent is released. At the same time, the higher the Tg, the greater the final viscosity of the resin reaction, and the better the solvent resistance and corrosion resistance after the paint is applied.
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